She began her career with the Inner London Education Authority, as a management trainee from 1984 to 1985 and a Policy Officer from 1985 to 1987.[4] She was head of the Women's Unit at the National Union of Students from 1988 to 1989, before joining Lambeth Council as an Equal Opportunities Officer from 1989 to 1991, and then Welfare and Staff Development Officer from 1991 to 1993.[4] From 1994 to 1997, she was the Senior Researcher and Political Officer for the GMB Union.[4]

As Public Health minister she was responsible for managing government programmes concerning radiation exposure, the potential bird flu epidemic, sex education, and the prevention of communicable diseases such as TB and HIV, and oversaw campaigns to tackle obesity, type 2 diabetes, heart disease, and cancer. She was also due to take ministerial responsibility for implementing the smoke-free workplace regulations in all public places resulting from the Health Act 2006, but was moved just a couple of days before it came into force (on 1 July 2007).

During her tenure at the Home Office, Flint reclassified magic mushrooms as a Class A drug.[7] Flint pushed through the bill[8] despite some challenges and objections from peers and MPs such as Dr Brian Iddon,[9][10] plus disputed use of a scientific study by Swiss academic Dr Felix Hasler,[11][12]

On 24 January 2008, Flint was promoted to Minister of State for Housing and Planning, and as a result would now attend Cabinet meetings.[3] She was also appointed a member of the Privy Council and she relinquished her role as regional minister.[3] In February 2008, Flint suggested that unemployed council tenants should "actively seek work", as a condition of their occupancy.[13] In May that year, she inadvertently revealed grim forecasts for the future of house prices when she was photographed walking into Downing Street with her briefing papers visible. Close inspection revealed that her document read: "We can't tell how bad it will get."[14]

She was moved to the Foreign and Commonwealth Office in the October 2008 reshuffle, to become the Minister for Europe.[1]
On 31 March 2009 she admitted that she had not read the Lisbon Treaty, the document which codifies the rules of the European Union. Critics described her admission as "extraordinary" and "unbelievable," particularly given that the minister's responsibilities include overseeing the introduction of the Treaty.[15]

Flint resigned after the Cabinetreshuffle of 5 June 2009 asserting that Gordon Brown was running a "two-tier government", and believed that she had been treated as "female window dressing" though she had earlier professed her loyalty to the Prime Minister.[16] Flint renewed her attack on Gordon Brown in an Observer newspaper article on 7 June 2009, saying that she was not ashamed of a glamorous photoshoot which had upset Downing Street. She launched a broadside against the Prime Minister, complaining of "this constant pressure, this negative bullying".[17]

On 16 May 2015, Caroline Flint announced her intention to seek candidacy for the Labour Party deputy leadership election. Along with Tom Watson, she was seen as being a front runner in the contest.[18] By the time nominations closed on 17 June, Flint had gained 43 MP nominees, second only to Tom Watson, and more than enough to confirm her place in the ballot.[19]
Flint came third.

In Parliament, she is a member of the Public Accounts Committee and the Intelligence and Security Committee of Parliament, and is a former member of the Administration Committee, the Education Sub-committee, the Education & Employment Committee and the Modernisation of the House of Commons Committee.[20]

In 2005, Flint claimed her constituency home in Sprotbrough as her second home, and a house in outer London as her main home. She sold her outer London home to buy a flat in Victoria, London in 2006. To buy the flat, Flint claimed £1,000 solicitors fees and £12,750 in stamp duty on allowances; the Fees Office paid £7,700 of the claim. The Victoria flat became her second home and her constituency property her main residence.[21][22]

Flint was one of 98 MPs who voted in favour of legislation which would have kept MPs' expense details secret.[23] In an investigation into MPs claims she was ordered by Sir Thomas Legg to repay £572 in over-claimed expenses.[24]

Flint employs her husband as her Senior Parliamentary Assistant on a salary up to £40,000.[25] She was listed in articles in the Daily Telegraph and Guardian criticising the practice of MPs employing family members, on the lines that it promotes nepotism.[26][27] Although MPs who were first elected in 2017 have been banned from employing family members, the restriction is not retrospective - meaning that Flint's employment of her husband is lawful.[28]

Flint's first marriage was to Saief Zammel, a Tunisian stockbroker.[29][30] They had a son, Karim, and a daughter, Hanna. Flint obtained a divorce in 1990 after Zammel was arrested on charges of violent disorder and was subsequently deported.[30][31]

In July 2001 she married her longtime boyfriend, Phil Cole, a former Labour Party regional officer and public relations professional who has been a councillor for the Edlington and Warmsworth ward of Doncaster Council since May 2012. They live in Flint's Don Valley constituency, in Sprotborough with three adult children from their former relationships.[32][33]